An organic electroluminescent (EL) light emitting apparatus includes organic EL devices, each of which has thin films and is of a self-emission type, and is applied as a new type flat panel display. Each of the organic EL devices is based on the following principle. That is, electrons are injected from a cathode into an organic layer and holes are injected from an anode into the organic layer, thereby generating excitons in an emission layer of the organic layer. Then, when the excitons return to the ground state, light is emitted from the emission layer. The emission layer is made of a fluorescent organic compound, a phosphorescent organic compound, or a light emitting material such as a quantum dot.
A challenge in developing the organic EL light emitting apparatus as described above is the improvement of light emitting efficiency. The organic EL device normally has a structure in which the anode, the organic layer including the emission layer, and the cathode are one-dimensionally laminated. In this case, a refractive index of the emission layer (approximately 1.5 to 2.0) is larger than a refractive index of air. Therefore, a majority of light emitted from an inner portion of the emission layer is totally reflected at a laminated film boundary whose refractive index changes from a high refractive index to a low refractive index. The totally reflected light becomes guided-wave light propagating in a direction parallel to a substrate, and then is confined to an inner portion of the organic EL device. A ratio of light which can be extracted for use to the outside (light extraction efficiency) is normally approximately 20%.
Therefore, in order to improve the light emitting efficiency of the organic EL light emitting apparatus, it is important to improve the light extraction efficiency.
Conventionally, it has been proposed to provide a periodic structure (such as sub-wavelength periodic structure or diffraction grating) in an upper or lower portion of a functional layer (on light extraction side or opposite side thereto) in order to prevent total reflection to suppress optical confinement in the inner portion of the organic EL device (see U.S. Pat. No. 5,779,924 and Japanese Patent Application Laid-Open No. 2004-349111).
Another method has been proposed in which, in order to reflect, in a light extraction direction, light which is confined as guided-wave light to the inner portion of the organic EL device and leaked from a side surface of the organic EL device, an inclined metal reflective surface is provided on the side surface of the organic EL device to improve light extraction efficiency (see Japanese Patent Application Laid-Open No. H11-214163).
When the periodic structure is provided in the upper portion of the functional layer as in the technologies described in U.S. Pat. No. 5,779,924 and Japanese Patent Application Laid-Open No. 2004-349111, there is a problem that the functional layer is damaged during a process of producing the periodic structure. When the periodic structure is provided in the lower portion of the functional layer, there is a problem that the thickness of the functional layer becomes nonuniform because of the unevenness of the periodic structure to locally change an interval between electrodes, and hence a short circuit occurs or a non-light emission point is generated.
The technology described in Japanese Patent Application Laid-Open No. H11-214163 has a problem that the distance between the electrodes is changed between a central portion and a peripheral portion of the organic EL device because of the inclination of the metal electrode, and hence a reduction in device endurance due to local light emission or an increase in number of non-light emitting devices due to a short circuit between electrodes occurs.